1. Field of the Invention
This invention relates to a technique for preventing loss of redundancy and performance deterioration of a writing process in a storage device having a plurality of cache memory modules.
2. Description of the Related Art
In the conventional storage device, a method is available to guarantee redundancy by a complete mirroring technique for a cache module.
A disk array device includes a plurality of disk modules for storing data, a plurality of memory modules for temporarily storing data at the time of writing or reading the data to and from the disk modules, and a plurality of director modules for controlling write or read operations, wherein the first and third memory modules are paired and so are the second and fourth memory modules. Upon occurrence of a fault in any one of the first to fourth memory modules, the first write data is written in paired one of the remaining memory modules by the director modules. Further, a cache management area is set in the two of the remaining memory modules. For the disk array device, therefore, a technique has been proposed in which the data write process is executed at high speed while at the same time avoiding data loss (Japanese Patent Application No. 2001-134487).
The conventional method poses a problem, however, that once any one of the cache modules fails, the redundancy is lost and the performance greatly deteriorates.
Specifically, in FIG. 1, in the case where cache 0 fails, cache data 0 in cache 1 becomes non-redundant. Next, in order to prevent the loss of cache data 0 at the time of failure of cache 1, the operation of cache 1 is suspended after writing cache data 0 into a disk.
As a result, only caches 2 and 3 are available for use, thereby greatly lowering both the read and write performance.